Solar Water Heating

Solar water heating is one of the most common uses of solar energy. Solar hot water collectors heat water for washing, showers, and other domestic uses. Over 100,000 of them have been installed in the United States.

In a solar hot water system, collector tubes inside an insulated box absorb the sun's heat and transfer the heat to water or another liquid flowing through the tubes. In areas where freezing is not a threat, the system can be an "open loop" where the water flowing through the tubes is heated directly for use. In colder areas the system is a "closed loop." Antifreeze liquid is heated before transferring its heat to the water by way of a heat exchanger. When you need hot water inside the house, the system draws on this heated water for your use.

Passive solar water heating is even simpler. There are two types of systems. The simplest is called a "batch water heater." The unit is located on the roof or on the ground near the house so that sun striking the collector goes directly into the storage tanks, where it heats the water. The hot water then flows downward into the home.

The other type of passive system is a "Thermosphon" unit, in which a storage tank is located on the roof above the collectors. As the water in the collectors is heated and becomes lighter, it naturally rises into the tank above it. The heavier cold water sinks to the lowest point in the system, which is the collector.

One easy way to figure out whether a solar water-heating system might be right for you is to use the US Department of Energy‚s Solar Benefits Model (www.eren.doe.gov/solarbuildings/sbm.html). The model uses a Microsoft Excel 97 spreadsheet to help you estimate the economic benefits of installing a solar water-heating system in a new home.